SEPTEMBER, 1962
NOTES
P-Terpinene and p-Phellandrene from the Pyrolysis of Sabinene 13. M. MITZNER AND E. T. THEIMER
3359
by n.m.r. and infrared as p-phellandrene, identical wit,h I11 isolated from a natural ~ o u r c e . ~ Experimental
Research Laboratories, Tntmnalional Flavors & Fragrances Trrc., Union Beach, New Jersey Received April 6, 1962
The only reported synthesis of 6-terpinene (I) is that of Wallach2 in five steps from sabinene (11). p-Phellandrene (111) has not been unequivocally synt,hesized, but is found in n a t ~ r e . ~ We have observed that 11, when pyrolyzed a t 600°, undergoes fission of the cyclopropane ring and forms I and 111:
Oil of savin was fractionated through a 2-ft. stainless steel protruded packed column, yielding sabinene-b.p. 45” :it 10 mm. and was analyzed pure by gas chromatography. This was passed four times through a 1 ft. X ]/E in. o.d., 2/32 inch i.d., stainless steel tube heated to 600°, a t a rate of 1 ml./min. A small flow of nitrogen was eniployed ae a carrier. The pyrolyzate was then separated into its components on a preparative gas chromatograph using a 3/8 in. 0.d. column packed with Reoplex 400 (207,) on 60-80 mesh silane treated Celite a t 100’. In this way, 8-terpinene and 8-phellandrene and unconverted sabinene are easily separable. We have found that it is essential that a non-acid type of solid support be used, otherwise a- and yterpinene will be formed from the 8-terpinene. p-Terpinene polymerizes in a matter of hours, especially when pure.
Acknowledgment.-The authors wish to acknowledge the aid given to them by Dr. S. Lemberg, of this laboratory, for his aid in the preparat,ion and interpretation of the n.m.r. spectra. I1
L
IV
A
I
I11
We postulate t,he biradical IV as an intermediate. The pyrolyzate from sabinene consists of a mixture of products including two major components, gas chromatographically eluted after the unconverted sabinene in an approximate ratio of 6:4. N.m.r. and infrared analysis confirm the structure of the first of these two peaks as P-terpinene. The n.m.r. spectrum of the p-terpinene indicated the following (in r values, tetramethylsilane, T = 10.00): 9.03, doublet, J c H ~H, 6 c.P.s., isopropyl group; 7.95, 7.87, 7.76, diffuse multiplet, allylic methylene; 7.28 multiplet, CH2 flanked by allylic double bonds; 5.36 singlet vinylidene methylene, > C = CHZ; 4.70 singlet, ring olefinic proton. The infrared spectrum of p-terpinene is characterized by a strong absorption a t 883 due to the >C=CHZ group which is also found in 1,(7) p-menthene. A medium band is observed a t 812 R* RB
(4) p-Phellandrene isolated from gum turpentine, and purified oio preparative gas chromatography. The sample wao graciously s u p plied by Mr. Ray V. Laurence, Chief, Naval Stores Laboratory: Olustee, Florida.
Absence of Asymmetric Induction in the Lithium Aluminum Hydride-&Camphor Reduction of Ketones PHILIP S. PORTOGHESE Department of Pharmaceutical Chemistry, College of Pharmacy, University of Minnesota, Minneapolis 14, Minnesota Received April 9, 1962
The exact mechanism of the reduction of ketones to secondary alcohols by lithium aluminum hydride is not known with certainty. I n an effort to elucidate the mode of hydride transfer to an electrophilic \ / cm.-1 which is due to the C=C group and center, we have employed the procedure of Bothner-By’ in which he has reported the preparation of / \ optically active secondary alcohols by reduction of R2 H is also found in 3, p-menthene. The split at 1375 the corresponding ketones. According to his ern.-’ is characteristic of the “gem” dimethyl group procedure, one equivalent of lithium aluminum hydride is reacted with two equivalents of d-camphor CHs whereupon the introduction of an unsymmetrical \/ C (found in both 1,(7) p-menthene as well ketone such as 2-butanone or pinacolone supposedly affords optically active 2-butanol or methyl-& /\ CHa butylcarbinol, respectively. I n repeating his exa s 3,p-menthenel. The second peak was identified perimental procedure we have observed no evidence of asymmetric induction in the hydride (1) a-Terpinene has not been positively identified in natural reduction of 2-butanone and pinacolone. materials. .r
(2) 0. Wallach. Ann., 867, 69 (1907). (3) J. L. Simonaen, “The Terpenes,” Vol. I, Cambridge, England,
University Press, 1963, p. 204.
(1) A. A. Bothner-By, J . Am. Cham. S O O . , ~ ? 846 ~ , (1951).
